This invention relates to alumina and products manufactured therefrom and more particularly, it relates to improved alumina catalyst supports and method of making stabilized alumina dispersions for forming into catalyst supports.
Alumina catalyst supports are made from concentrated dispersions of alumina powders in water. However, properties of such alumina catalyst supports can suffer as a result of poorly dispersed alumina. For example, alumina catalyst supports can have a less uniform pore structure and can have a surface roughness that can vary during extrusion of the dispersion. Such defects result in a less effective alumina catalyst. These problems often result from the colloidal instability and the related viscosity instability of concentrated alumina dispersions. That is, the viscosity of concentrated alumina powder dispersions can increase significantly as a result of particle aggregation or coagulation, and this can lead to non-uniformity problems in the catalyst support. Further, particle aggregation in concentrated alumina dispersions can result in gellation which can render the alumina dispersions useless.
In the extrusion of alumina dispersions that is performed in the manufacture of catalyst supports, some alumina dispersions will not extrude or extrude poorly, resulting in an extrudate that breaks or cracks during extrusion if the viscosity of the dispersion is not maintained within certain ranges. Also, various properties of the extrudate, such as the extrudate surface area and pore volume distribution, are affected by the stability and related properties of the alumina dispersion. Accordingly, there is a great need for an improved process for making catalyst supports utilizing stabilized alumina dispersions in order to provide for improved properties in the catalyst supports.
Briefly, alumina catalyst supports are manufactured from concentrated alumina dispersions by extruding, drying and firing. Such steps are set forth in U.S. Pat. No. 4,301,037, incorporated herein by reference.
Dispersants have been used in various applications including the manufacture of aluminum oxide tubes and dishwater detergents. For example, U.S. Pat. No. 5,059,367 discloses a process for the manufacture of aluminum oxide tubes involving grinding and spraying aluminum oxide wherein a first grinding of aluminum oxide is carried out until gas tightness can be achieved in later firing at 1720.degree.-1769.degree. C. Further, the patent discloses that this is achieved at a mean particle diameter below 15 .mu.m, particularly from 2 to 5 .mu.m. The spraying is preferably carried out after the addition of a binder that results in a uniform powder with only a small proportion of very fine material. The water soluble stabilizing agent is usually an organic compound which decomposes during the sintering process without leaving a residue. According to the patent, compounds that may be used for this purpose are polyvinyl alcohol, polyvinyl acetate dispersions or polyethylene glycol. Further, these compounds increase the viscosity of solutions and prevent the high-density aluminum oxide from settling out.
In preparing liquid dishwater detergents, an abrasive scouring cleanser containing bleach and aluminum oxide thickeners are employed. U.S. Pat. No. 5,279,755 discloses a thickened aqueous suspension that serves as an abrasive scouring cleanser containing bleach and stably suspended abrasives in an aqueous suspension comprising a colloidal aluminum oxide thickener and at least one surfactant which can, in association with aluminum oxide under alkaline conditions, provide proper theology and cleaning. The suspension includes an electrolyte, a halogen bleach, a particulate abrasive and a phase stabilizing amount of a multivalent metal salt of C.sub.16-22 fatty acid. The surfactant is selected from anionic, bleach-stable nonionic, amphoteric, zwitterionic surfactants and preferred is a combination of anionics and bleach-stable nonionics. The anionic surfactants are selected from bleach-stable surfactants such as alkali metal alkyl sulfates, secondary alkane sulfonates, alkyl diphenyl ether disulfonates, fatty acids and mixtures thereof.
U.S. Pat. No. 4,950,416 discloses an aqueous thixotropic automatic dishwater detergent containing a thickener constituted from an alumina dispersion and a stabilizer consisting of either a long chain fatty acid, a metal salt of a long chain fatty acid or mixtures thereof. The dishwater detergent contains water, sodium silicate, alkali metal phosphate, chlorine bleach compound, a bleach stable, water-dispersible organic detergent active material, and a thickener consisting of an aqueous alumina dispersion with a stabilizer of a mixture of a long chain fatty acid and the polyvalent metal salt of a long chain fatty acid. The preferred surfactant is an alkyl diphenoloxide mono- and/or di-sulfonates.
U.S. Pat. No. 3,867,296 discloses a process for preparing clear bright oleaginous aluminum dispersions that involves admixing an oil-soluble dispersing agent, an oleaginous carrier and a volatile solvent with a dispersible alumina, and then heating and recovering the oleaginous aluminum dispersion. In U.S. Pat. No. 5,039,550, there is disclosed an alumina/water dispersion having a pH of 11 to which is added a polyacrylate dispersant at a concentration of about 0.1 wt. % of alumina powder. According to the patent, the polyacrylate dispersant is primarily in ionic form at the pH of the solution and the dispersant is attached to the alumina particles by hydrogen bonding between surface hydroxyl sites and carboxyl groups on the surfactant.
Other dispersants or surfactants are referred to in U.S. Pat. Nos. 5,300,255; 4,391,718; 4,721,579; 4,898,685; 5,063,257 and 5,135,844.